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WDM (Wavelength Division Multiplexing) is to combine a series of optical carrier signals at different wavelengths carrying various information at the transmitter through the Multiplexer and couple them to the same optical fiber for transmission.  At the receiver end, the optical signals are separated from each other by a Demultiplexer. The simultaneous transmission of two or many optical signals of different wavelengths in the same fiber is called Wavelength Division Multiplexing (WDM). WDM technology can double the transmission capacity of a single light, which can easily expand the capacity of existing optical networks. Depending on the direction of the transmitted signal, WDM can be used for multiplexing or demultiplexing.




The main function of MUX is to combine multiple signal wavelengths into one optical fiber for transmission. At the transmitter end, N optical transmitters operate at N different wavelengths, which are separated by appropriate intervals. These N light waves are respectively modulated by the signal as carriers and carry the signal. A wave synthesizer combines these different wavelengths of optical carrier signals and couples them into a single-mode fiber. Because the optical carrier signals of different wavelengths can be regarded as independent of each other (without considering the non-linearity of the fiber), the multiplexing transmission of multiple optical signals can be realized in one fiber. Through multiplexing, communication operators can avoid maintaining multiple lines and effectively save operating costs.




The main function of DEMUX is to separate multiple wavelength signals transmitted in one fiber. At the receiving end, the optical carrier signals of different wavelengths are separated by a demultiplexer, which is further processed by the optical receiver to recover the original signal. A demultiplexer (Demux) is a device that performs reverse processing on a multiplexer.  


Performance Parameters of MUX/DEMUX


1. Operating Wavelength


Multiplexer/demultiplexer operating waveband. For example, 1550 wavelength has three bands: S band (short wavelength band 1460~1528nm), C band (conventional band 1530~1565nm), L band (long wavelength band 1565~1625nm).


2. Number of channels & channel spacing


Channel number refers to the number of channels that a multiplexer/demultiplexer can combine or separate. This number can range from 4 to 160 to enhance the design by adding more channels. Common channels are 4, 8, 16, 32, 40, 48, etc. Channel spacing is the difference between the nominal carrier frequencies of two adjacent channels and is used to prevent inter-channel interference. According to ITU-T G.692, the channel intervals less than 200GHz(1.6nm) include 100GHz (0.8nm), 50GHz (0.4nm) and 25GHz. Currently, 100GHz and 50GHz channel intervals are preferred.


3. Insertion Loss


Insertion loss is the attenuation caused by the insertion of WDM in optical transmission system. The attenuation effect of WDM on optical signal directly affects the transmission distance of the system. Generally, the lower the insertion loss, the less signal attenuation.


4. Isolation


Isolation refers to the isolation degree between signals of each channel. High isolation values can effectively prevent the distortion of transmitted signals caused by crosstalk between signals.


5. PDL (Polarization Dependent Loss)


PDL refers to the distance between the maximum and minimum loss caused by different polarization states at fixed temperature, wavelength and the same band, namely, the maximum deviation of insertion Loss in all input polarization states. 

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